Led luminaire driving circuit and method

ABSTRACT

A resonant converter is provided with a plurality of secondary transformer windings. A first secondary winding provides a fixed output, which is utilized to control the switching frequency of the resonant converter. A second secondary winding drives one or more LED luminaires, and is provided with a secondary side resonant circuit. When the feedback from the first output calls for a reduced frequency so as to increase the output, the reduced frequency results in an increased impedance of the secondary side resonant circuit so as to prevent any voltage rise for the LED luminaires. When the feedback from the first output calls for an increased frequency so as to reduce the output, the increased frequency results in an decreased impedance of the secondary side resonant circuit so as to prevent any voltage fall for the LED luminaires.

TECHNICAL FIELD

The present invention relates to the field of light emitting diode (LED)drivers, and in particular to an arrangement wherein a single secondarywinding is utilized to provide both a fixed output and drive for atleast one LED based luminaire.

BACKGROUND OF THE INVENTION

LED based luminaires are rapidly replacing both incandescent andfluorescent luminaires for both general lighting and backlightingapplications. In large liquid crystal based monitors, and in large solidstate lighting applications, such as street lighting and signage,typically the LEDs are supplied in one or more strings of seriallyconnected LEDs, which thus share a common current. A plurality ofparallel strings may also be supplied.

The power supply which is to drive the LEDs preferably also suppliespower to the operating circuitry of the device, thus reducing cost.Typically a single power supply comprising a power transformer with aplurality of secondary windings is utilized, the primary stage of whichis controlled by a feedback circuit to provide a fixed direct current(DC) voltage for the operating circuitry of the device through aparticular one of the secondary windings.

A resonant converter is a switching converter that comprises a tankcircuit actively participating in determining input to output powerflow. Power flow in a resonant converter is typically controlled eitherby changing the switching frequency, or the duty cycle, or both. In oneembodiment two reactive elements, i.e. a capacitor and an inductor formthe tank circuit, and such a resonant inverter is known as an LCinverter. A resonant converter comprises a resonant inverter, which hasa switching network and a resonant tank circuit, and a rectifiercircuit.

A resonant converter having two inductive elements, and a singlecapacitor in the tank circuit, where one of the inductive elements isarranged in parallel with the load, and another inductive element is inseries with the load and the capacitor, is known as an LLC converter.Advantageously, an LLC converter exhibits a pair of resonant peaks, eachassociated with a particular one of the inductors. When properlydesigned, an LLC converter can be simply controlled by adjusting thefrequency responsive to an output feedback, as long as the operatingfrequency is kept between the two resonant peak frequencies. Typically,a drop in output is compensated for by decreasing the operatingfrequency, and an increase in output is compensated for by increasingthe operating frequency.

In a typical embodiment, the two inductors are implemented in anintegrated transformer having a leakage inductance where the inductanceof the primary winding acts as the parallel inductive element and theleakage inductance acts as the series inductive element. The transformerfurther enables scaling of the design output voltage based on the turnsratio of the primary and secondary windings of the integratedtransformer.

In order to reduce cost, it is desired to have a single converterprovide drive for both the LEDs and for the operating circuits of thedevice. Since the voltage for the operating circuits of the device mustbe well regulated, the LED drive voltage is not well regulated. Onesolution of a circuit 10 for driving at least one LED luminaire offeredby the prior art is illustrated in FIG. 1. Circuit 10 comprises: a powersource 20; a resonant mode controller 30, optionally comprising an LLCcontroller; a converter 40 comprising a bridge circuit 50, a primaryside capacitance element CP and a transformer 60; a pair ofunidirectional electronic valves D1; a unidirectional electronic valveD2; an inductance element 70; a capacitance element C1; a capacitanceelement C2; an electronically controlled switch SS; a plurality of LEDluminaires, denoted respectively L1, L2 and L3; a plurality ofelectronically controlled switches SL; a plurality of sense resistiveelements RS; an LED controller 80; a pair of unidirectional electronicvalves D3; a voltage divider 110; and a reference voltage source 120.Bridge circuit 50 comprises a pair of electronically controlledswitches, denoted respectively SB1 and SB2. Transformer 60 comprises: aprimary winding 130; and a plurality of secondary windings, denotedrespectively 140, 150 and 160.

In one embodiment, primary side capacitance element CP, capacitanceelement C1 and capacitance element C2 are each implemented as acapacitor, and are described herein as such. In another embodiment,unidirectional electronic valves D1, D2 and D3 are each implemented as adiode, and are described herein as such. In one embodiment, inductanceelement 70 is implemented as an inductor, and is described herein assuch. In another embodiment, each sense resistive element RS isimplemented as a resistor, and is described herein as such. In oneembodiment, electronically controlled switches SB1, SB2, SS and SL areeach implemented as an n-channel metal-oxide-semiconductorfield-effect-transistor (NFET), and are described herein as such.

The output of power source 20 is coupled to the drain of NFET SB1 andthe return of power source 20 is coupled to the source of NFET SB2. Thegates of NFETs SB1, SB2 are each coupled to a respective output ofresonant mode controller 30. The source of NFET SB1 is coupled to thedrain of NFET SB2 and a first end of primary side capacitor CP. A secondend of primary side capacitor CP is coupled to a first end of primarywinding 130 of transformer 60 of converter 40. A second end of primarywinding 130 is coupled to the return of power source 20. A first andsecond end of secondary winding 140 of transformer 60 are each coupledto the anode of a respective one of pair of diodes D1 and the center tapof secondary winding 140 is coupled to a common potential.

The cathodes of diodes D1 are each coupled to a first end of inductor 70and to a first end of capacitor C1. The second end of capacitor C1 iscoupled to the common potential. The second end of inductor 70 iscoupled to the drain of NFET SS and the anode of diode D2. The source ofNFET SS is coupled to the common potential and the gate of NFET SS iscoupled to an output of LED controller 80. The cathode of diode D2 iscoupled to a first end of capacitor C2 and the anode end of each of LEDluminaires L1, L2, L3. The second end of capacitor C2 is coupled to thecommon potential. The cathode end of each of LED luminaires is coupledto the drain of a respective NFET SL and to a respective input of LEDcontroller 80. The source of each NFET SL is coupled to a first end of arespective sense resistor RS and a respective input of LED controller80. The second end of each sense resistor RS is coupled to the commonpotential and the gate of each NFET SL is coupled to a respective outputof LED controller 80.

Secondary winding 150 is coupled to a respective load (not shown). Eachend of secondary winding 160 is coupled to the anode of a respectivediode D3 and the center tap of second winding 160 is coupled to thecommon potential. The cathode of each diode D3 is coupled to a load (notshown) and a first end of voltage divider 110. A second end of voltagedivider 110 is coupled to the common potential and a division junctionof voltage divider 110 is coupled to a respective input of resonant modecontroller 30. The output of reference voltage source 120 is coupled toa respective input of resonant mode controller 30 and the return ofreference voltage source 120 is coupled to the common potential.

In operation, resonant mode controller 30 is arranged to alternatelyopen and close NFETs SB1 and SB2 such that primary winding 130 ischarged when NFET SB1 is closed and discharged when NFET SB2 is closed.Resonant mode controller 30 typically operates at a fixed duty cycle ofnear 50%, with a variable frequency, as will be described further. Thepower supplied to transformer 60 is controlled via secondary winding 160and voltage divider 110. Particularly, when NFET SB1 is closed andprimary winding 130 is charging, power is output from secondary winding160 via a first diode D3. When NFET SB2 is closed and primary winding130 is discharging, power is output from secondary winding 160 via thesecond diode D3. The rectified voltage at the cathodes of diodes D3 issupplied to the load and is additionally divided by voltage divider 110.The divided voltage is compared to the reference voltage output byreference voltage source 120. In the event that the divided voltage ishigher than the output of reference voltage source 120, resonant modecontroller 30 is arranged to increase the switching frequency of bridgecircuit 50 thereby reducing the amount of power supplied to secondarywinding 160. In the event that the divided voltage is lower than theoutput of voltage source 120, resonant mode controller 30 is arranged toreduce the switching frequency of bridge circuit 50 thereby increasingthe amount of power supplied to secondary winding 160.

Secondary winding 140 is similarly influenced by the control of resonantmode controller 30. Since the voltage across secondary winding 140 isnot independently controlled, the voltage appearing across capacitor C2needs to be controlled so as to provide an appropriate operating voltagefor LED luminaires L1, L2, L3. The operation of inductor 70, NFET SS anddiode D2 act as a boost converter to increase the output voltage ofsecondary winding 140, stored across capacitor C1. Particularly, whenNFET SS is closed, inductor 70 is charged by secondary winding 140. WhenNFET SS is open, capacitor C2 is charged and LED luminaires L1, L2, L3are powered by the combination of the power supplied by secondarywinding 140 and the power stored on inductor 70. LED luminaires L1, L2,L3 are thus powered at a voltage greater than the voltage provided bysecondary winding 140. LED controller 80 is arranged to detect thevoltage at the cathode end of each LED luminaire L1, L2, L3 and comparethe detected voltages to a predetermined reference voltage. In the eventthat one or more of the detected voltages are lower than thepredetermined reference voltage, i.e. the voltage across capacitor C2 isless than the optimal operating voltages of at least one of LEDluminaires L1, L2, L3, LED controller 80 is arranged to increase theduty cycle of the boost converter, i.e. increase the percentage of timethat NFET SS is closed. The voltage across capacitor C2 thus increases.

The current flowing through each of LED luminaires L1, L2, L3 generatesa voltage across the respective sense resistor RS, which is detected byLED controller 80. In one embodiment, LED controller 80 is arranged toadjust the pulse width modulation (PWM) duty cycle of each NFET SL tocontrol the current flowing through each LED luminaire L1, L2, L3. Inanother embodiment, LED controller 80 is arranged to adjust the gatevoltage of each NFET SL to thereby adjust the current flowing throughthe respective one of LED luminaires L1, L2, L3, by increasing theeffective voltage drop across the respective NFET SL. Any excess poweris dissipated across the NFET SL. LED controller 80 may be a single unitcontrolling both NFET SS and the respective NFET SLs, or may be separatecontrol units without exceeding the scope.

Another solution of a circuit 200 for driving at least one LED luminaireoffered by the prior art is illustrated in FIG. 2. Circuit 200comprises: power source 20; resonant mode controller 30; converter 40comprising bridge circuit 50, primary side capacitor CP and transformer60; capacitor C1; diode D2; inductor 70; capacitor C2; LED luminaire L1;NFET SL; sense resistor RS; LED controller 80;

voltage divider 110; reference voltage source 120; and a pair ofrectifier bridges, denoted respectively 210 and 220. A single LEDluminaire is illustrated, however this is not meant to be limiting inany way and any number of LED luminaires may be provided. Bridge circuit50 comprises NFETs SB1 and SB2. Transformer 60 comprises: primarywinding 130; and plurality of secondary windings 140, 150 and 160. Inone embodiment, rectifier bridges 210 and 220 are each implemented as adiode bridge, and are described herein as such.

The output of power source 20 is coupled to the drain of NFET SB1 andthe return of power source 20 is coupled to the source of NFET SB2. Thegates of NFETs SB1, SB2 are each coupled to a respective output ofresonant mode controller 30. The source of NFET SB1 is coupled to thedrain of NFET SB2 and a first end of primary side capacitor CP. A secondend of primary side capacitor CP is coupled to a first end of primarywinding 130 of transformer 60 of converter 40. A second end of primarywinding 130 is coupled to the return of power source 20.

Each end of secondary winding 140 of transformer 60 is coupled to arespective input of diode bridge 210 and the return of diode bridge 210is coupled to a common potential. The output of diode bridge 210 iscoupled to a first end of capacitor C1, the cathode of diode D2 and afirst end of inductor 70. The second end of capacitor C1 is coupled tothe common potential. The second end of inductor 70 is coupled to afirst end of capacitor C2 and the anode end of LED luminaire L1. Thesecond end of capacitor C2 is coupled to the anode of diode D2, thecathode end of LED luminaire L1 and the drain of NFET SL. The source ofNFET SL is coupled to a first end of sense resistor RS and an input ofLED controller 80. The second end of sense resistor RS is coupled to thecommon potential and the gate of NFET SL is coupled to an output of LEDcontroller 80.

Secondary winding 150 is coupled to a respective load (not shown), oralternatively not provided. Each end of second winding 160 is coupled toa respective input of diode bridge 220 and the return of diode bridge220 is coupled to the common potential. The output of diode bridge 220is coupled to a load (not shown) and a first end of voltage divider 110.A second end of voltage divider 110 is coupled to the common potentialand a division junction of voltage divider 110 is coupled to arespective input of resonant mode controller 30. The output of referencevoltage source 120 is coupled to a respective input of resonant modecontroller 30 and the return of reference voltage source 120 is coupledto the common potential.

In operation, resonant mode controller 30 is arranged to alternatelyopen and close NFETs SB1 and SB2, typically at a predetermined dutycycle near 50%. Primary winding 130 is charged when NFET SB1 is closedand discharged when NFET SB2 is closed. The voltage output across diodebridge 200 is controlled by resonant mode controller 30, as describedabove. Particularly, the voltage across secondary winding 160, rectifiedby diode bridge 220, is supplied to the load, typically across an outputcapacitor (not shown) and is additionally divided by voltage divider110. The divided voltage is compared to the voltage output by referencevoltage source 120. In the event that the divided voltage is higher thanthe output of reference voltage source 120, resonant mode controller 30is arranged to increase the switching frequency of bridge circuit 50thereby reducing the amount of power supplied to secondary winding 160.In the event that the divided voltage is lower than the output ofvoltage source 120, resonant mode controller 30 is arranged to reducethe switching frequency of bridge circuit 50 thereby increasing theamount of power supplied to secondary winding 160.

The output by secondary winding 140 is similarly impacted by theoperation of resonance mode controller 30, and thus the voltage acrosscapacitor C1 changes responsive to changes in the load of secondarywinding 160. The operation of inductor 70, diode D2 and NFET SL act as abuck converter to reduce the output voltage of secondary winding 140,stored across capacitor C1 to the appropriate voltage for LED luminaireL1. Particularly, when NFET SL is closed, power is provided to LEDluminaire L1 by secondary winding 140 and inductor 70 is charged bysecondary winding 140. When NFET SL is open, LED luminaire L1 is poweredby the power stored on inductor 70. LED luminaire L1 is thus powered ata voltage less than the voltage provided by secondary winding 140responsive to the duty cycle of NFET SL as controlled by LED controller80.

The current flowing through LED luminaire L1 generates a voltage acrossthe respective sense resistor RS, which is detected by LED controller80. LED controller 80 is arranged to adjust the pulse width modulation(PWM) duty cycle of NFET SL to control the current flowing through LEDluminaire L1. Additionally, the PWM adjustment of NFET SL adjusts theduty cycle of the buck converter of inductor 70, diode D2 and NFET SL,thus adjusting the voltage provided to LED luminaire L1 accordingly.

Advantageously, a resonant LED luminaire driving circuit, such as theabove described LLC converter circuits 10 and 200, automaticallyprovides for zero voltage switching for the LLC switching elements.However, the above converter circuits 10, 200 require an additionalinductor 70. Additionally, NFETs SS and SL are operated in hardswitching mode. What is desired, and not provided by the prior art, isan integrated converter which provides both a regulated voltage for useby operating circuits, and a regulated LED drive voltage, withoutrequiring the additional inductors, dissipative regulators, or hardswitching of the prior art.

SUMMARY OF THE INVENTION

Accordingly, it is a principal object of the present invention toovercome at least some of the disadvantages of the prior art. This isprovided in one embodiment by a first circuit for driving at least onelight emitting diode (LED) luminaire, the circuit comprising: a resonantmode controller; a converter comprising a transformer having a primarywinding and a plurality of secondary windings each magnetically coupledto the primary winding, a bridge circuit arranged to switch responsiveto the resonant mode controller, and a primary side capacitor coupled tothe primary winding; a first output associated with a first of theplurality of secondary windings, the resonant mode controller arrangedto adjust the switching frequency of the bridge circuit so as tomaintain the first output at a predetermined level; a second outputassociated with a second of the plurality of secondary windings; asecondary side capacitance element arranged in series between the secondof the plurality of secondary windings and the second output; an LEDcontroller; a first LED luminaire arranged to provide a firstillumination responsive to a power signal on the second output; and afirst current regulator arranged to regulated current flowing throughthe first LED luminaire responsive to the LED controller.

In another embodiment, a second circuit for driving an LED luminaire isprovided, the second circuit comprising: a primary side controller; aflyback converter comprising a transformer having a primary winding anda plurality of secondary windings each magnetically coupled to theprimary winding, and a primary electronically controlled switch, theprimary electronically controlled switch arranged to alternately openand close responsive to the primary side controller, the open and closedstate arranged to adjust a current flowing through the primary winding;a first output associated with a first of the plurality of secondarywindings, the primary side controller arranged to alternately open andclose the primary electronically controlled switch so as to maintain thefirst output at a predetermined voltage level; a first unidirectionalelectronic valve arranged between the first secondary winding and thefirst output; a second output associated with a second of the pluralityof secondary windings; an LED controller; a first secondaryelectronically controlled switch arranged to be alternately in a closedstate and an open state responsive to the LED controller; and a firstLED luminaire coupled to the second output and arranged in cooperationwith the first secondary electronically controlled switch so as toprovide a first illumination responsive to a power signal on the secondoutput when the first secondary electronically controlled switch is in afirst of the open and closed states and not provide the firstillumination when the first secondary electronically controlled switchis in a second of the open and closed states wherein the turns ratio ofthe first secondary winding and the second secondary winding is suchthat power is delivered to the first output via the first unidirectionalelectronic valve only when the first secondary electronically controlledswitch is switched to the second of the open and closed states.

Additional features and advantages of the invention will become apparentfrom the following drawings and description.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the invention and to show how the same maybe carried into effect, reference will now be made, purely by way ofexample, to the accompanying drawings in which like numerals designatecorresponding elements or sections throughout.

With specific reference now to the drawings in detail, it is stressedthat the particulars shown are by way of example and for purposes ofillustrative discussion of the preferred embodiments of the presentinvention only, and are presented in the cause of providing what isbelieved to be the most useful and readily understood description of theprinciples and conceptual aspects of the invention. In this regard, noattempt is made to show structural details of the invention in moredetail than is necessary for a fundamental understanding of theinvention, the description taken with the drawings making apparent tothose skilled in the art how the several forms of the invention may beembodied in practice. In the accompanying drawing:

FIG. 1 illustrates a high level schematic diagram of a boost mode LEDluminaire driving circuit, according to the prior art;

FIG. 2 illustrates a high level schematic diagram of a buck mode LEDluminaire driving circuit, according to the prior art;

FIG. 3A illustrates a high level schematic diagram of a synchronous buckmode LED luminaire driving circuit, according to certain embodiments;

FIGS. 3B-3C illustrate waveforms of certain components of the LEDluminaire driving circuit of FIG. 3A;

FIG. 4A illustrates a high level schematic diagram of a synchronous buckmode LED luminaire driving circuit, comprising a plurality of LEDluminaires, according to certain embodiments;

FIG. 4B illustrates waveforms of certain components of the LED luminairedriving circuit of FIG. 4A;

FIG. 5 illustrates a high level schematic diagram of a first embodimentof a synchronous boost mode LED luminaire driving circuit, according tocertain embodiments;

FIG. 6A illustrates a high level schematic diagram of a secondembodiment of a synchronous boost mode LED luminaire driving circuit,according to certain embodiments;

FIG. 6B illustrates waveforms of certain components of the LED luminairedriving circuit of FIG. 6A;

FIG. 7A illustrates a high level schematic diagram of a fly-back modeLED luminaire driving circuit, according to certain embodiments;

FIG. 7B illustrates waveforms of certain components of the LED luminairedriving circuit of FIG. 7A;

FIG. 8A illustrates a high level schematic diagram of a fly-back modeLED luminaire driving circuit, comprising a plurality of LED luminaires,according to certain embodiments;

FIG. 8B illustrates waveforms of certain components of the LED luminairedriving circuit of FIG. 8A;

FIGS. 9A-9B illustrate a high level flow chart of a first embodiment ofan LED luminaire driving method, according to certain embodiments; and

FIGS. 10A-10B illustrate a high level flow chart of a second embodimentof an LED luminaire driving method, according to certain embodiments.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Before explaining at least one embodiment of the invention in detail, itis to be understood that the invention is not limited in its applicationto the details of construction and the arrangement of the components setforth in the following description or illustrated in the drawings. Theinvention is applicable to other embodiments or of being practiced orcarried out in various ways. Also, it is to be understood that thephraseology and terminology employed herein is for the purpose ofdescription and should not be regarded as limiting.

FIG. 3A illustrates a high level schematic diagram of an LED luminairedriving circuit 300, according to certain embodiments. Circuit 300comprises: power source 20; resonant mode controller 30; converter 40comprising bridge circuit 50, primary side capacitor CP and transformer60; a secondary side capacitance element CS; voltage divider 110;reference voltage source 120; diode bridge 210; diode bridge 220; an LEDcontroller 305; capacitor C2; a capacitance element C3; LED luminaireL1; NFET SL; sense resistor RS; and a plurality of resistive elementsR1, R2, R3 and R4. A single LED luminaire is illustrated, however thisis not meant to be limiting in any way and any number of LED luminairesmay be provided without exceeding the scope. Bridge circuit 50 comprisesNFETs SB1 and SB2. Transformer 60 comprises: primary winding 130; andsecondary windings 140, 150 and 160, with secondary winding 150 beingoptional. Secondary winding 140 exhibits a leakage inductance 310 inseries therewith. In one embodiment, each of resistive elements R1, R2,R3 and R4 are implemented as resistors, and are described herein assuch. The combined resistance of resistors R3 and R4 equals the combinedresistance of resistors R1 and R2. Secondary side capacitance CS andcapacitance element C3 are each in one embodiment implemented as acapacitor, and are described herein as such.

The output of power source 20 is coupled to the drain of NFET SB1 andthe return of power source 20 is coupled to the source of NFET SB2. Thegates of NFETs SB1, SB2 are each coupled to a respective output ofresonant mode controller 30. The source of NFET SB1 is coupled to thedrain of NFET SB2 and a first end of primary side capacitor CP. A secondend of primary side capacitor CP is coupled to a first end of primarywinding 130 of transformer 60 of converter 40. A second end of primarywinding 130 is coupled to the return of power source 20.

A first end of secondary winding 140 is coupled to a first end ofleakage inductance 310, and a second end of leakage inductance 310 iscoupled to a first end of secondary side capacitor CS. The second end ofsecondary side capacitor CS is coupled to a first input of diode bridge210, a first end of resistor R1 and a first end of capacitor C3, denotednode VS. The second end of secondary winding 140 is coupled to a secondinput of diode bridge 210, a second end of capacitor C3 and a first endof resistor R3. A second end of resistor R1 is coupled to a first end ofresistor R2 and a respective input of LED controller 305. A second endof resistor R2 is coupled to a common potential. A second end ofresistor R3 is coupled to a first end of resistor R4 and a second end ofresistor R4 is coupled to the common potential. The return of diodebridge 210 is coupled to the common potential. The output of diodebridge 210, denoted OUT2, is coupled to a first end of capacitor C2 andthe anode end of LED luminaire L1. The second end of capacitor C2 iscoupled to the cathode end of LED luminaire L1 and the drain of NFET SL.The source of NFET SL is coupled to a first end of sense resistor RS anda respective input of LED controller 305. The second end of senseresistor RS is coupled to the common potential and the gate of NFET SLis coupled to an output of LED controller 305.

Optional secondary winding 150 is coupled to a respective load (notshown). Each end of secondary winding 160 is coupled to a respectiveinput of diode bridge 220 and the return of diode bridge 220 is coupledto the common potential. The output of diode bridge 220, denoted OUT1,is coupled across an output capacitor to a load (not shown) and a firstend of voltage divider 110. A second end of voltage divider 110 iscoupled to the common potential and a division junction of voltagedivider 110 is coupled to a respective input of resonant mode controller30. The output of reference voltage source 120 is coupled to arespective input of resonant mode controller 30 and the return ofreference voltage source 120 is coupled to the common potential.

In operation, resonant mode controller 30 is arranged to alternatelyopen and close NFETs SB1 and SB2, typically at a predetermined dutycycle near 50%. The primary winding 130 is charged when NFET SB1 isclosed and discharged when NFET SB2 is closed. The voltage appearingacross the load coupled to secondary winding 160 is controlled via thefeedback path of voltage divider 110, as described above. Particularly,the voltage across secondary winding 160, rectified by diode bridge 220,is supplied to the load and is additionally divided by voltage divider110. The divided voltage is compared to the voltage output by referencevoltage source 120. In the event that the divided voltage is higher thanthe output of reference voltage source 120, resonant mode controller 30is arranged to increase the switching frequency of bridge circuit 50thereby reducing the amount of voltage to the load coupled to secondarywinding 160. In the event that the divided voltage is lower than theoutput of voltage source 120, resonant mode controller 30 is arranged toreduce the switching frequency of bridge circuit 50 thereby increasingthe amount of voltage to the load couplet to secondary winding 160.

Secondary winding 140 is similarly impacted by the change in frequencyof resonant mode controller 30. Leakage inductance 310 and secondaryside capacitor CS form a resonant circuit 320. Transformer 60 andsecondary side capacitor CS are provided such that the resonantfrequency of resonant circuit 320 is greater than the maximum switchingfrequency of converter 40. As a result, when resonant mode controller 30reduces the switching frequency of converter 40, in order to increasethe voltage at secondary winding 160, the switching frequency becomesfurther distanced from the resonant frequency of resonant circuit 320and as a result the impedance of resonant circuit 320 increases. Thus,the increase in electrical energy caused by the reduction in switchingfrequency is compensated for by the increased impedance of resonantcircuit 320 and the rectified voltage at output OUT2 of diode bridge 210doesn't appreciably increase.

Similarly, when resonant mode controller 30 increases the switchingfrequency of converter 40, in order to reduce the voltage at secondarywinding 160, the switching frequency approaches the resonant frequencyof resonant circuit 320, and as a result the impedance of resonantcircuit 320 decreases. Thus, the decrease in electrical energy caused bythe increase in switching frequency is compensated for by the reducedimpedance of resonant circuit 320 and the rectified voltage at outputOUT2 of diode bridge 210 doesn't appreciably decrease.

The current flowing through LED luminaire L1 generates a voltage acrosssense resistor RS, which is detected by LED controller 305. LEDcontroller 305 is arranged to adjust the pulse width modulation (PWM)duty cycle of NFET SL to control the current flowing through LEDluminaire L1 responsive to the detected voltage drop across senseresistor RS. LED controller 305 is arranged to be synchronized with thevoltage across secondary winding 160, as illustrated in FIGS. 3-3C wherethe x-axis represents time and the y-axis represents voltage inarbitrary units. The voltage across secondary winding 140, stored acrosscapacitor C3, is denoted VS and illustrated by graph 400 in FIGS. 3B-3C.Voltage VS is divided by resistors R1 and R2, the divided voltagereceived by LED controller 305. In one embodiment, the gate voltage ofNFET SL, denoted VG and illustrated by graph 410 of FIG. 3B, issynchronized with voltage VS with leading edge modulation, as will bedescribed below. In another embodiment, the gate voltage of NFET SL,denoted VG and illustrated by graph 420 of FIG. 3C, is synchronized withvoltage VS with trailing edge modulation, as will be described below.

For leading edge modulation, as illustrated in FIG. 3B, NFET SL isopened when voltage VS, illustrated by graph 400, is zero. At time T1,NFET SB1 is closed and voltage VS rises to the positive operatingvoltage. At time T2, LED controller 305 is arranged to output a highgate voltage VG to NFET SL, illustrated by graph 410, thereby closingNFET SL and allowing current to flow through LED luminaire L1. At timeT3, NFET SB1 is opened and voltage VS begins to fall responsive to theopening of NFET SB1. Additionally, the inductive current stored inleakage inductance 310 of secondary winding 140 starts flowing, i.e.freewheeling, through LED luminaire L1 and decays. At time T4, when bothNFET SB1 and NFET SB2 are opened, voltage VS becomes zero. NFET SB1 andNFET SB2 are maintained in an open position for a predetermined timeperiod to avoid a condition where NFET SB1 and NFET SB2 are closed atthe same time, thereby short circuiting power source 20, a conditionknown as shoot through. At time T5, LED controller 305 is arranged toswitch gate voltage VT to a low gate voltage VG for NFET SL therebyopening NFET SL when substantially zero voltage is presentedthereacross, thereby reducing switching losses. Additionally,transformer 60 is designed such that leakage inductance 310 is of anappropriate value so that the inductive current thereof decays to zero,or near-zero, at time T5, thus realizing a soft switching operation,i.e. switching at zero voltage and zero current. At time T6, NFET SB2 isclosed and voltage VS begins to fall. At time T7, voltage VS falls tothe negative operating voltage and at time T8 LED controller 305 isarranged to switch gate voltage VG to a high gate voltage VG forapplication to NFET SL. At time T9, NFET SB1 is opened and voltage VSbegins to rise responsive to NFET SB1 being opened. At time T10, whenboth NFET SB1 and SB2 are opened, voltage VS becomes zero. At time T11,LED controller 305 is arranged to switch the output gate voltage VG alow gate voltage for application to NFET SL thereby opening NFET SL whensubstantially zero voltage is presented thereacross. At time T12, NFETSB1 is closed and voltage VS begins to rise. At time T13 voltage VSrises to the positive operating voltage and at time T14 LED controller305 is arranged to switch the output gate voltage VG to high forapplication to NFET SL.

For trailing edge modulation, illustrated in FIG. 3C, NFET SL is closedwhen voltage VS, illustrated by graph 400, is zero. At time T1, NFET SB1is closed and voltage VS rises to the positive operating voltage. Attime T2, LED controller 305 is arranged to output a low gate voltage VGto NFET SL, illustrated by graph 420, thereby opening NFET SL andpreventing current from flowing through LED luminaire L1. At time T3,NFET SB1 is opened and voltage VS begins to fall responsive to theopening of NFET SB1. At time T4, when both NFET SB1 and NFET SB2 areopened, voltage VS becomes zero. NFET SB1 and NFET SB2 are maintained inan open position for a predetermined time period to avoid shoot-throughcondition where NFET SB1 and NFET SB2 are closed at the same time,thereby short circuiting power source 20. At time T5, LED controller 305is arranged to switch the output gate voltage VG to a high value forapplication to NFET SL thereby closing NFET SL when substantially zerovoltage is presented, thus resulting in soft switching. At time T6, NFETSB2 is closed and voltage VS begins to fall. At time T7, voltage VSfalls to the negative operating voltage and at time T8 LED controller305 is arranged to switch the output gate voltage VG to a low value forapplication to NFET SL, thereby opening NFET SL. The inductive currentof leakage inductance 310 of secondary winding 140 thus freewheelsthrough capacitor C3 and secondary side capacitor CS, the storedinductive energy of leakage inductance 310 being transferred tocapacitor C3 and secondary side capacitor CS as the freewheeling currentdegrades. At time T9, NFET SB1 is opened and voltage VS begins to riseresponsive to the opening of NFET SB1 opens. At time T10, when both NFETSB1 and SB2 are opened, voltage VS becomes zero. At time T11, LEDcontroller 305 is arranged to switch the output gate voltage VG to ahigh value for application to NFET SL thereby closing NFET SL whensubstantially zero voltage is presented thereacross. At time T12, NFETSB1 is closed and voltage VS begins to rise. At time T13 voltage VSrises to the positive operating voltage and at time T14 LED controller305 is arranged to switch the output gate voltage VG to a low value forapplication to NFET SL, thereby opening NFET SL. The inductive currentof leakage inductance 310 of secondary winding 140 thus freewheelsthrough capacitor C3 and secondary side capacitor CS, the storedinductive energy of leakage inductance 310 being transferred tocapacitor C3 and secondary side capacitor CS as the freewheeling currentdegrades.

Resistors R3 and R4 are arranged to balance the resistance provided byresistors R1 and R2, such that the resistance at the inputs of diodebridge 210, i.e. across both ends of secondary winding 140 are equal.Resistors R3 and R4 are illustrated as being separate resistors, howeverthis is not meant to be limiting in any way and in another embodimentthe combined resistance of resistors R3 and R4 is provided by a singleresistor.

Advantageously, as opposed to LED luminaire driving circuits 10, 200,LED luminaire driving circuit 300 does not include a secondary sideinductor 70. Particularly, the buck function is provided by NFET SL,sense resistor RS and leakage inductance 310 of secondary winding 140.Additionally, NFET SL is either switched to be opened, or switched to beclosed, when substantially zero voltage is presented thereacross. Thus,soft switching occurs at one of the two switching transitions.

The above has been described in an embodiment where the illumination ofLED luminaire L1 is regulated by pulse width modulation switching ofNFET SL, however this is not meant to be limiting in any way. In anotherembodiment (not shown), the current flowing through LED luminaire L1 isregulated by linear regulation of NFET SL, thereby adjusting the voltagedrop across NFET SL.

FIG. 4A illustrates a high level schematic diagram of an LED luminairedriving circuit 500, according to certain embodiments. LED luminairedriving circuit 500 is in all respects similar to LED luminaire drivingcircuit 300 of FIG. 3A, with the exception that a plurality of LEDluminaires are provided, denoted respectively L1, L2 and L3. Each one ofLED luminaires L1, L2, L3 has associated therewith a respective one of aplurality of NFETs, denoted respectively SL1, SL2 and SL3, a respectiveone of a plurality of unidirectional electronic valves D0 and arespective one of a plurality of sense resistors RS. In one embodiment,each of the plurality of unidirectional electronic valves DO comprises adiode, and is described herein as such. The anode of each diode DO iscoupled to the cathode end of the respective one of LED luminaires L1,L2, L3, and the cathode of each diode D0 is coupled to the drain of therespective one of NFETs SL1, SL2, SL3. Diodes D0 prevent cross bleedingof capacitors C2 when more than one of NFETs SL1, SL2, SL3 aresimultaneously in a closed state. The operation of LED luminaire drivingcircuit 500 is in all respects similar to the operation of LED luminairedriving circuit 300 of FIG. 3A, with the exception that the NFETs SL1,SL2 are each driven with trailing edge modulation and NFET SL3 is drivenwith leading edge modulation, as illustrated in FIG. 4B where the x-axisrepresents time and the y-axis represents voltage in arbitrary units.The voltage across secondary winding 140 of transformer 60, storedacross capacitor C3, is denoted VS and illustrated by graph 400 of FIG.4B. The gate voltage of NFET SL1 is denoted VG1 and illustrated by graph510 of FIG. 4B. The gate voltage of NFET SL2 is denoted VG2 andillustrated by graph 520 of FIG. 4B. The gate voltage of NFET SL3 isdenoted VG3 and illustrated by graph 530 of FIG. 4B.

LED controller 305 is arranged to determine which one of LED luminairesL1, L2, L3 exhibits the highest operating voltage, by detecting thevoltage across the respective sense resistor RS. The highest operatingvoltage will result in the lowest current flowing through the respectivesense resistor RS. In another embodiment (not shown), a respective inputof LED controller 305 is coupled to the cathode end of each of LEDluminaires L1, L2, L3, LED controller 305 arranged to directly measurethe operating voltages of LED luminaires L1, L2, L3. The respective oneof NFETs SL1, SL2, SL3 associated with the LED luminaire exhibiting thehighest operating voltage is driven with leading edge modulation and theother NFETs are driven with trailing edge modulation. For clarity, thebelow will be described in an embodiment where LED luminaire L3 exhibitsthe highest operating voltage, however this is not meant to be limitingin any way.

As illustrated in FIG. 4B, at time T1, NFET SB1 is closed and voltage VSrises to the positive operating voltage. Gate voltages VG1 and VG2 arehigh and therefore NFETs SL1 and SL2 are closed and current flowsthrough LED luminaires L1 and L2. At time T2, LED controller 305 isarranged to switch the output gate voltage VG3 to high for applicationto NFET SL3 thereby closing NFET SL3. Since LED luminaire L3 exhibits ahigher operating voltage than LED luminaires L1 and L2, the voltagethereacross will not be sufficient to power LED luminaire L3 until bothLED luminaires L1 and L2 are turned off, however the overlapping of ontime of LED luminaire L3 with the on time of LED luminaires L1 and L2will allow the continuation of the flow of inductive current of leakageinductance 310 of secondary winding 140 to through LED luminaire L3,instead of capacitor C3 and secondary side capacitor CS, and thusminimizing the energy circulation loss and switching stress when LEDluminaires L1 and L2 are turned off.

At time T3, LED controller 305 is arranged to switch the output gatevoltage VG1 to a low state for application to NFET SL1 thereby openingNFET SL1 and preventing current from flowing through LED luminaire L1.At time T4, LED controller 305 is arranged to switch the output gatevoltage VG2 to a low state for application to NFET SL2 thereby openingNFET SL2 and preventing current from flowing through LED luminaire L2.The voltage across LED luminaire L3 rises responsive to the currentdrive from secondary winding 140 to the necessary operating voltage forLED luminaire L3 and current flows therethrough. At time T5, NFET SB1 isopened and voltage VS begins to fall responsive to the opening of NFETSB1. At time T6, when both NFET SB1 and NFET SB2 are opened, voltage VSbecomes zero. NFET SB1 and NFET SB2 are maintained in an open positionfor a predetermined time period to avoid a shoot-through condition. Attime T7, LED controller 305 is arranged to switch the output gatevoltage VG3 to a low state for application to NFET SL3 thereby openingNFET SL3 when substantially zero voltage is presented thereacross. Attime T8, LED controller 305 is arranged to switch the output gatevoltage VG1 to a high state for application to NFET SL1 and to switchthe output gate voltage VG2 to a high state for application to NFET SL2thereby closing NFETs SL1 and SL2 when substantially zero voltage ispresented thereacross. In one embodiment, NFETs SL1 and SL2 can beclosed at any time between T7 and T9.

At time T9, NFET SB2 is closed and voltage VS begins to fall. At timeT10, voltage VS falls to the negative operating voltage and at time T11LED controller 305 is arranged to switch the output gate voltage VG3 toa high state for application to NFET SL3 thereby closing NFET SL3. Attime T12, LED controller 305 is arranged to switch the output gatevoltage VG1 to a low state for application to NFET SL1 thereby openingNFET SL1 and preventing current from flowing through LED luminaire L1.At time T13, LED controller 305 is arranged to switch the output gatevoltage VG2 to a low state for application to NFET SL2 thereby openingNFET SL2 and preventing current from flowing through LED luminaire L2.The voltage across LED luminaire L3 thus rises to the necessaryoperating voltage and current flows therethrough.

At time T14, NFET SB1 is opened and voltage VS begins to rise responsivethereto. At time T15, when both NFET SB1 and SB2 are opened, voltage VSbecomes zero. At time T16, LED controller 305 is arranged to switch theoutput gate voltage VG3 to a low state for application to NFET SL3thereby opening NFET SL3 when substantially zero voltage is presentedthereacross. At time T17, LED controller 305 is arranged to switch theoutput gate voltage VG1 to a high state for application to NFET SL1 andto switch the output voltage VG2 to a high state for application to NFETSL2 thereby closing NFETs SL1 and SL2 when substantially zero voltage ispresented thereacross. At time T18, NFET SB1 is closed and voltage VSbegins to rise. At time T19 voltage VS rises to the positive operatingvoltage and at time T20 LED controller 305 is arranged to switch theoutput gate voltage VG3 to a high state for application to NFET SL3,thus closing NFET SL3.

FIG. 5 illustrates a high level schematic diagram of an LED luminairedriving circuit 600, according to certain embodiments. LED luminairedriving circuit 600 comprises: power source 20; resonant mode controller30; converter 40 comprising bridge circuit 50, primary side capacitor CPand transformer 60; secondary side capacitor CS; voltage divider 110;voltage source 120; diode bridge 210; diode bridge 220; an LEDcontroller 605; capacitor C2; LED luminaire L1; NFET SS; sense resistorRS; diode D2; and resistors R1, R2, R3 and R4. A single LED luminaire isillustrated, however this is not meant to be limiting in any way and anynumber of LED luminaires may be provided without exceeding the scope.Bridge circuit 50 comprises NFETs SB1 and SB2. Transformer 60 comprises:primary winding 130; and secondary windings 140, 150 and 160. Secondarywinding 140 exhibits leakage inductance 310.

The output of power source 20 is coupled to the drain of NFET SB1 andthe return of power source 20 is coupled to the source of NFET SB2. Thegates of NFETs SB1, SB2 are each coupled to a respective output ofresonant mode controller 30. The source of NFET SB1 is coupled to thedrain of NFET SB2 and a first end of primary side capacitor CP. A secondend of primary side capacitor CP is coupled to a first end of primarywinding 130 of transformer 60 of converter 40. A second end of primarywinding 130 is coupled to the return of power source 20.

A first end of secondary winding 140 is coupled to a first end ofleakage inductance 310, and a second end of leakage inductance 310 iscoupled to a first end of secondary side capacitor CS. The second end ofsecondary side capacitor CS is coupled to a first input of diode bridge210 and a first end of resistor R1. The second end of secondary winding140 is coupled to a second input of diode bridge 210 and a first end ofresistor R3. A second end of resistor R1 is coupled to a first end ofresistor R2 and a respective input of LED controller 605. A second endof resistor R2 is coupled to a common potential. A second end ofresistor R3 is coupled to a first end of resistor R4 and a second end ofresistor R4 is coupled to the common potential. The return of diodebridge 210 is coupled to the common potential. The output of diodebridge 210, denoted OUT2, is coupled to the drain of NFET SS and theanode of diode D2. The source of NFET SS is coupled to the commonpotential and the gate of NFET SS is coupled to an output of LEDcontroller 605. The cathode of diode D2 is coupled to a first end ofcapacitor C2 and the anode end of LED luminaire L1. The second end ofcapacitor C2 is coupled to the common potential and the cathode end ofLED luminaire L1 is coupled to the common potential via sense resistorRS. The cathode end of LED luminaire L1 is further coupled to arespective input of LED controller 605.

Optional secondary winding 150 is coupled to a respective load (notshown). Each end of second winding 160 is coupled to a respective inputof diode bridge 220 and the return of diode bridge 220 is coupled to thecommon potential. The output of diode bridge 220, denoted OUT1, iscoupled to a load (not shown) and a first end of voltage divider 110. Asecond end of voltage divider 110 is coupled to the common potential anda division junction of voltage divider 110 is coupled to a respectiveinput of resonant mode controller 30. The output of reference voltagesource 120 is coupled to a respective input of resonant mode controller30 and the return of reference voltage source 120 is coupled to thecommon potential.

In operation, as described above in relation to LED luminaire drivingcircuit 300 of FIG. 3A, resonant mode controller 30 is arranged toalternately open and close NFETs SB1 and SB2, typically at apredetermined duty cycle near 50%, with a variable frequency, such thatprimary winding 130 is charged when NFET SB1 is closed and dischargedwhen NFET SB2 is closed. The voltage appearing across the load coupletto secondary winding 160 is controlled via the feedback path of voltagedivider 110, as described above. Particularly, the voltage acrosssecondary winding 160, rectified by diode bridge 220, is supplied to theload and is additionally divided by voltage divider 110. The dividedvoltage is compared to the voltage output by reference voltage source120. In the event that the divided voltage is higher than the output ofreference voltage source 120, resonant mode controller 30 is arranged toincrease the switching frequency of bridge circuit 50 thereby reducingthe amount of voltage to the load coupled to secondary winding 160. Inthe event that the divided voltage is lower than the output of referencevoltage source 120, resonant mode controller 30 is arranged to reducethe switching frequency of bridge circuit 50 thereby increasing theamount of voltage to the load coupled to secondary winging 160.

Secondary winding 140 is similarly impacted by the change in frequencyof resonant mode controller 30. Leakage inductance 310 and secondaryside capacitor CS form a resonant circuit 320. Transformer 60 andsecondary side capacitor CS are provided such that the resonantfrequency of resonant circuit 320 is greater than the maximum switchingfrequency of converter 40. As a result, when resonant mode controller 30reduces the switching frequency of converter 40, in order to increasethe voltage at secondary winding 160, the switching frequency becomesfurther distanced from the resonant frequency of resonant circuit 320and as a result the impedance of resonant circuit 320 increases. Thus,the increase in electrical energy caused by the reduction in switchingfrequency is compensated for by the increased impedance of resonantcircuit 320 and the rectified voltage at output OUT2 of diode bridge 210doesn't appreciably increase.

Similarly, when resonant mode controller 30 increases the switchingfrequency of converter 40, in order to reduce the voltage at secondarywinding 160, the switching frequency approaches the resonant frequencyof resonant circuit 320, and as a result the impedance of resonantcircuit 320 decreases. Thus, the decrease in electrical energy caused bythe increase in switching frequency is compensated for by the reducedimpedance of resonant circuit 320 and the rectified voltage at outputOUT2 of diode bridge 210 doesn't appreciably decrease.

The current flowing through LED luminaire L1 generates a voltage acrossthe respective sense resistor RS, which is detected by LED controller605. LED controller 605 is arranged to adjust the pulse width modulation(PWM) duty cycle of NFET SS to control the current flowing through LEDluminaire L1. Particularly, when NFET SS is closed, leakage inductance310 is charged through NFET SS to the common potential. When NFET SS isopen, leakage inductance 310 is charged through LED luminaire 310, thusincreasing the voltage at output OUT2 of diode bridge 210. In oneembodiment, NFET SS is driven with trailing edge modulation, responsiveto voltage VS divided by resistors R1 and R2 and received by LEDcontroller 605. When driven with trailing edge modulation, NFET SS isclosed when voltage VS is zero and leakage 310 has been completelydischarged through LED luminaire L1. As a result, NFET SS is closed whenzero voltage is presented thereacross. As described above, resistors R3and R4 are arranged to balance the resistance provided by resistors R1and R2, such that the resistance at the inputs of diode bridge 210 areequal.

FIG. 6A illustrates a high level schematic diagram of an LED luminairedriving circuit 700, according to certain embodiments. The arrangementof LED luminaire driving circuit 700 is in all respects similar to thearrangement of LED luminaire driving circuit 600 of FIG. 5 with theexception that diode bridge 210 is replaced with a pair of diodes D4, anelectronically controlled switch SS1 and an electronically controlledswitch SS2. Additionally, NFET SS and diode D2 are not provided. In oneembodiment, electronically controlled switch SS1 and electronicallycontrolled switch SS2 are each implemented as an NFET, and are describedherein as such. The anode of a first diode D4 is coupled to the secondend of capacitor CS, the first end of resistor R1 and the drain of NFETSS1. The source of NFET SS1 is coupled to the common potential and thegate of NFET SS1 is coupled to a respective output LED controller 605.The anode of the second diode D4 is coupled to the second end ofsecondary winding 140, the second end of leakage inductance 310, thefirst end of resistor R3 and the drain of NFET SS2. The source of NFETSS2 is coupled to the common potential and the gate of NFET SS2 iscoupled to a respective output of LED controller 605. The cathode ofeach of the first and second diode D4 is coupled to the first end ofcapacitor C2 and the anode end of LED luminaire L1.

The operation of LED luminaire driving circuit 700 is in all respectssimilar to the operation of LED luminaire driving circuit 600, with theexception that the charging and discharging of leakage inductance 310 iscontrolled via NFETs SS1, SS2, as illustrated in FIG. 6B, where thex-axis represents time and the y-axis represents voltage in arbitraryunits. The voltage across secondary winding 140 is denoted VS andillustrated by graph 400 of FIG. 6B. The gate voltage of NFET SS1 isdenoted VGS1 and illustrated by graph 710 of FIG. 6B. The gate voltageof NFET SS2 is denoted VGS2 and illustrated by graph 720 of FIG. 6B.

At time T1, NFET SB1 is closed and voltage VS rises to the positiveoperating voltage, gate voltages VGS1 and VGS2 being high at time T1.Leakage inductance 310 is thus being charged. At time T2, LED controller605 is arranged to output a low state gate voltage VGS1 to NFET SS1,thereby opening NFET SS1 and allowing current to flow through the firstdiode D4 to LED luminaire L1 with the return path supplied by NFET SS2.As a result, leakage inductance 310 begins to discharge. At time T3,NFET SB1 is opened and voltage VS begins to fall as NFET SB1 opens. Attime T4, when both NFET SB1 and NFET SB2 are opened, voltage VS becomeszero. NFET SB1 and NFET SB2 are maintained in an open position for apredetermined time period to avoid a shoot-through condition where NFETSB1 and NFET SB2 are closed at the same time, thereby short circuitingpower source 20. At time T5, LED controller 605 is arranged to switchgate voltage VGS2 to a low state for application to NFET SL2 therebyopening NFET SL2 when substantially zero voltage is presentedthereacross. In another embodiment (not shown), NFET SL2 is left closeduntil time T9 described below. At time T6, when VS is still zero, LEDcontroller 605 is arranged to respectively switch output gate voltagesVGS1, VGS2 to a high state for application to NFETs SL1, SL2, therebyforming a charging path for leakage inductance 310 in a directionopposing the charge direction of time T1. At time T7, NFET SB2 is closedand voltage VS begins to fall and starts charging leakage inductance 310in a negative direction opposing the charge direction of time T1. Attime T8, voltage VS falls to the negative operating voltage and thecharging of leakage inductance 310 continues. At time T9, LED controller605 is arranged to switch the output gate voltage VGS2 to a low statefor application to NFET SL2. Leakage inductance 310 is thus dischargedby powering LED luminaire L1 through second diode D4. At time T10, NFETSB2 is opened and voltage VS begins to rise as NFET SB2 opens.Additionally, LED controller 605 is arranged to switch the output gatevoltage VGS1 to a low state for application to NFET SL1. In anotherembodiment (not shown), NFET SL1 is left closed until time T15 describedbelow. At time T11, when both NFET SB1 and SB2 are opened, voltage VSbecomes zero. At time T12, LED controller 605 is arranged torespectively switch gate voltages VGS1, VGS2 to high states forapplication to NFETs SL1, SL2 thereby closing NFETs SL1 and SL2 whensubstantially zero voltage is presented thereacross. Leakage inductance310 thus begins to charge, as described above in relation to time T1. Attime T13, NFET SB1 is closed and voltage VS begins to rise. At time T14voltage VS rises to the positive operating voltage and at time T15 LEDcontroller 605 is arranged to switch gate voltage VGS1 to the low statefor application to NFET SL1, thereby powering LED luminaire L1 with thepower discharged from leakage inductance 310, as described above inrelation to time T2.

FIG. 7A illustrates a high level schematic diagram of an LED luminairedriving circuit 800, according to certain embodiments. LED luminairedriving circuit 800 comprises: power source 20; a primary sidecontroller 810; a converter 820 comprising a primary electronicallycontrolled switch SP and a transformer 840; a unidirectional electronicvalve D5; a capacitance element C4; voltage divider 110; voltage source120; resistors R1 and R2; a unidirectional electronic valve D6; an LEDcontroller 805; capacitor C2; LED luminaire L1; NFET SL; and senseresistor RS. A single LED luminaire is illustrated, however this is notmeant to be limiting in any way and any number of LED luminaires may beprovided without exceeding the scope. Transformer 840 comprises: aprimary winding 850; and a plurality of secondary windings, denotedrespectively 860, 870 and 880. In one embodiment, primary electronicallycontrolled switch SP is implemented as an NFET, and is described hereinas such. In another embodiment, unidirectional electronic valves D5 andD6 are each implemented as a diode, and are described herein as such. Inone embodiment, capacitance element C4 is implemented as a capacitor,and is described herein as such. The turns ratio of secondary winding860 and secondary winding 880 is a function of the ratio between theoperating voltage of LED luminaire L1 and the operating voltage of theload at an output OUT1 such that when LED luminaire L1 has currentflowing therethrough the voltage across secondary winding 860, denotedVS1, is less than the operating voltage of the load at output OUT1, aswill be described below.

The output of power source 20 is coupled to a first end of primarywinding 850 of transformer 840 and the second end of primary winding 850is coupled to the drain of NFET SP, the polarity of the second end ofprimary winding 850 denoted with a dot. The source of NFET SP is coupledto the return of power source 20 and the gate of NFET SP is coupled toan output of primary side controller 810. The anode of diode D5 iscoupled to a first end of secondary winding 860 of transformer 840, thepolarity thereof denoted with a dot. The cathode of diode D5 is coupledto a first end of capacitor C4, a first end of voltage divider 110 and aload (not shown), the node denoted OUT1. The second end of capacitor C4is coupled to a common potential and the second end of secondary winding860 is coupled to the common potential. A second end of voltage divider110 is coupled to the common potential and a voltage division node ofvoltage divider 110 is coupled to a respective input of primary sidecontroller 810. The output of reference voltage source 120 is coupled toa respective input of primary side controller 810 and the return ofreference voltage source 120 is coupled to the common potential.Optional secondary winding 870 of transformer 840 is coupled to arespective load (not shown).

A first end of secondary winding 880 of transformer 840 is coupled to afirst end of resistor R1 and the anode of diode D6, the polarity of thefirst end of secondary winding 880 denoted with a dot and the node isdenoted OUT2, carrying a signal VS2. A second end of resistor R1 iscoupled to a first end of resistor R2 and to a respective input of LEDcontroller 805. The second end of resistor R2 and the second end ofsecondary winding 880 are each coupled to the common potential. Thecathode of diode D6 is coupled to a first end of capacitor C2 and theanode end of LED luminaire L1. The second end of capacitor C2 is coupledto the cathode end of LED luminaire L1 and the drain of NFET SL. Thesource of NFET SL is coupled to a first end of sense resistor RS and arespective input of LED controller 805. The second end of sense resistorRS is coupled to the common potential and the gate of NFET SL is coupledto an output of LED controller 805.

The operation of LED luminaire driving circuit 800 is illustrated inFIG. 7B, where the x-axis represents time and the y-axis representsvoltage in arbitrary units. The current flowing through primary winding850 of transformer 840 is denoted IP and illustrated by graph 890 ofFIG. 7B. The voltage at node OUT2, denoted VS2, is illustrated by graph900 of FIG. 7B. The gate voltage of NFET SL, output by LED controller805, is denoted VG and illustrated by graph 910 of FIG. 7B.

At time T1, NFET SP is closed and current IP is increasing. Due to thepolarity of primary winding 850 and secondary windings 860 and 880,voltage VS2 is equal to a negative voltage, and therefore no currentflows through diode D6. Additionally, gate voltage VG is low and NFET SLis open. At time T2, LED controller 805 is arranged to output a highgate voltage VG to NFET SL, thereby closing NFET SL, however no currentflows there through due to the blocking action of diode D6. LEDcontroller 805 is arranged to detect voltage VS2, divided by resistorsR1 and R2, so as to close NFET SL when voltage VS2 is not greater thanzero. At time T3, primary side controller is arranged to open NFET SP.As a result, current IP begins to decrease and the voltage acrossprimary winding 850 reverses, thereby causing a reversal of voltage VS2,which now forward biases diode D6, and voltage VS2 rises to theoperating voltage of LED luminaire L1, denoted VL in FIG. 7B. Asdescribed above, the turns ratio of secondary windings 860 and 880 issuch that when voltage VS2 equals VL, the voltage across secondarywinding 860, denoted VS1, is less than the operating voltage of the loadof output OUT1, and therefore diode D5 is reverse biased. For example,if the voltage at output OUT1 and stored across capacitor C4 is 12V andthe operating voltage of LED luminaire L1 is less than 12V, secondarywinding 880 may exhibit the same number of turns as secondary winding860. If the operating voltage of LED luminaire L1 is 12V, secondarywinding 880 may exhibit a greater number of turns than secondary winding860. As a result, as described above, the potential at the anode ofdiode D5 is less than the potential at the cathode thereof when diode D6is conducting, thereby no power is provided to capacitor C4 and outputOUT1. The operation of LED luminaire L1 prevents voltage VS2 from risingabove LED luminaire operating voltage VL, thereby preventing voltage VS1from rising further.

LED controller 805 is arranged to compare the current flowing throughLED luminaire L1, responsive to the voltage across sense resistor RS,with a predetermined current level. When the current exceeds thepredetermined current level, at time T4 LED controller 805 is arrangedto switch gate voltage VG to a low state for presentation to NFET SL,thereby opening NFET SL. Voltage VS1 across secondary winding 860 is nolonger restricted by operating voltage VL of LED luminaire L1 and cancontinue rising to the operating voltage of the load at output OUT1.Voltage VS2 across secondary winding 880 also rises, as illustrated,however NFET SL is open and the increased voltage does not impact LEDluminaire L1. Current IP continues to decrease at a rate responsive tothe power supplied to OUT1. At time T5, current IP reaches zero andprimary winding 850 is completely discharged, thereby presenting arespective zero voltage VS1 and VS2 across secondary windings 860 and880. At time T6, primary side controller 810 is arranged to close NFETSP, with substantially zero voltage presented thereacross, therebycausing current IP to rise and voltage VS2 to fall to a negativevoltage, as described above. At time T7, LED controller 805 is arrangedto switch gate voltage VG to a high state for presentation to NFET SL,as described above in relation to time T2. Since diode D6 is reverselybiased by a negative voltage when primary side NFET SP is closed, theclosing (turn on) time of NFET SL can be arranged at any point betweenT1 and T2, or T6 and T7, without affecting the circuit operation. Attime T8, primary side controller 810 is arranged to open NFET SP, asdescribed above in relation to time T3. Advantageously, LED luminairedriving circuit 800 allows regulation of the voltage at output OUT1without affecting the operation of LED luminaire L1. Additionally, NFETSL is closed when zero voltage is presented thereacross.

FIG. 8A illustrates a high level schematic diagram of an LED luminairedriving circuit 1000, according to certain embodiments. LED luminairedriving circuit 1000 is in all respects similar to LED luminaire drivingcircuit 800 of FIG. 7A, with the exception that a plurality of LEDluminaires L1, L2 are provided. Each of the plurality of LED luminairesL1, L2 has associated therewith a diode D6, a capacitor C2, a senseresistor RS and a respective one of a pair of NFETs SL1 and SL2.Additionally, transformer 840 further comprises a second primary winding1010, and converter 820 further comprises a voltage divider 1020associated with second primary winding 1010.

The anode end of each of LED luminaires L1, L2 is coupled to a first endof the respective capacitor C2 and the cathode of the respective diodeD6, the anode of each diode D6 coupled to node OUT2. The cathode end ofeach of LED luminaires L1, L2 is coupled to a second end of therespective capacitor C2 and the drain of the respective one of NFETsSL1, SL2. The source of each of NFETs SL1, SL2 is coupled to the commonpotential via the respective sense resistor RS and to a respective inputof LED controller 805. The gate of each of NFETs SL1, SL2 is coupled toa respective output of LED controller 805. A first end of primarywinding 1010 of transformer 840 is coupled to a first end of voltagedivider 1020, the polarity of the first end of primary winding 1010denoted with a dot. A voltage division node of voltage divider 1020 iscoupled to a respective input of primary side controller 810. A secondend of voltage divider 1020 and the second end of primary winding 1010are each coupled to a primary side common potential.

The operation of LED luminaire driving circuit 1000 is illustrated inFIG. 8B, where the x-axis represents time and the y-axis representsvoltage in arbitrary units. The current flowing through primary winding850 of transformer 840 is denoted IP and illustrated by graph 1030 ofFIG. 8B. The voltage at node OUT2 is denoted VS2 and illustrated bygraph 1040 of FIG. 8B. The gate voltage of NFET SL1, output by LEDcontroller 805, is denoted VG1 and illustrated by graph 1050 of FIG. 8B.The gate voltage of NFET SL2, output by LED controller 805, is denotedVG2 and illustrated by graph 1060 of FIG. 8B.

At time T1, NFET SP is closed and current IP is increasing. Due to thepolarity of primary winding 850 and secondary windings 860 and 880, andthe respective diodes D5 and D6, voltage VS2 is equal to a negativevoltage and no current flows through the output secondary windings 860,880. Additionally, gate voltages VG1 and VG2 are low and thus NFETs SL1and SL2 are open. At time T2, LED controller 805 is arranged torespectively switch gate voltages VG1 and VG2 to a high state forpresentation to NFETs SL1 and SL2, thereby closing NFETs SL1 and SL2.LED controller 805 is arranged to detect voltage VS2, divided byresistors R1 and R2, so as to close NFETs SL1, SL2 when voltage VS2 isnot greater than zero. At time T3, primary side controller 810 isarranged to open NFET SP. As a result, current IP begins to decrease andthe voltage across primary winding 850 reverses, thereby causing areversal of voltage VS2 to the operating voltage of LED luminaire L1,denoted VL1 in FIG. 8B. As described above, the turns ratio of secondarywindings 860 and 880 is such that when voltage VS2 equals VL1, thevoltage across secondary winding 860 is less than the operating voltageof the load of output OUT1. As a result, the potential at the anode ofdiode D5 is less than the potential at the cathode thereof, thereby notproviding power to capacitor C4 and output OUT1. The operation of LEDluminaire L1 prevents voltage VS2 from rising above LED luminaireoperating voltage VL1, thereby preventing voltage VS1 from rising.

LED controller is arranged to compare the current flowing through LEDluminaire L1, responsive to the voltage across the respective senseresistor RS, with a predetermined current level. When the currentexceeds the predetermined current level, at time T4 LED controller 805is arranged to switch gate voltage VG1 to a low state for presentationto NFET SL1, thereby opening NFET SL1. Voltage VS2 then continues torise until reaching the operating voltage of LED luminaire L2, denotedVL2 in FIG. 8B, and current flows through LED luminaire L2. LEDcontroller 805 is arranged to compare the current flowing through LEDluminaire L2, responsive to the voltage across the respective senseresistor RS, with a predetermined current level. When the currentexceeds the predetermined current level at time T5. LED controller 805is arranged to output a low state gate voltage VG2 to NFET SL2, therebyopening NFET SL2. The voltage across secondary winding 860 is no longerrestricted by operating voltage VL1 of LED luminaire L1, or operatingvoltage VL2 of LED luminaire L2 and thus rises to the operating voltageof the load at output OUT1 until diode D5 is forward biased. Responsiveto the increase in voltage across secondary winding 860, voltage VS2across secondary winding 880 also rises, as illustrated. However, NFETsSL1 and SL2 are open and the increased voltage does not impact LEDluminaires L1, L2. Current IP continues to decrease as power is fed tothe load coupled to OUT1.

At time T6, current IP reaches zero and primary winding 850 iscompletely discharged. The drain voltage of NFET SP begins to oscillatealong the down slope and primary side controller 810 is arranged todetect the drain voltage of NFET SP, reflected to primary winding 1010and divided by voltage divider 1020, as known to those skilled in theart of quasi-resonant switching. When the drain voltage of NFET SPreaches a low valley peak, primary side controller 810 is arranged toclose NFET SP, with minimal voltage thereacross, thereby causing currentIP to rise and voltage VS2 to fall to a negative voltage, as describedabove. At time T7, LED controller 805 is arranged to switch gatevoltages VG1 and VG2 to a high state for presentation to NFET SL1 andNFET SL2, as described above in relation to time T2. Since diode D6 isreversely biased by a negative voltage when primary side NFET SP isclosed, the closing (turn on) time of NFETs SL1 and SL2 can be arrangedat any point between T1 and T2, or T6 and T7, without affecting thecircuit operation. At time T8, primary side controller 810 is arrangedto open NFET SP, as described above in relation to time T3.Advantageously, LED luminaire driving circuit 1000 allows regulation ofthe voltage at output OUT1 without affecting the operation of LEDluminaires L1, L2. Additionally, NFETs SL1 and SL2 are each closed whensubstantially zero voltage is presented thereacross.

FIGS. 9A-9B illustrate a high level flow chart of a first LED luminairedriving method, according to certain embodiments. In stage 1100, abridge circuit is switched so as to produce a first output power signal,associated with a first of a plurality of secondary windings of atransformer. Each of the plurality of secondary windings of thetransformer is magnetically coupled to the primary winding of thetransformer. The primary winding of the transformer is coupled in seriesto a primary side capacitor.

In stage 1110, the frequency of the bridge circuit switching of stage1100 is controlled so as to maintain the first output power signal at apredetermined level, by reducing the switching frequency responsive to afalling first output power signal and increasing the switching frequencyresponsive to a rising first output power signal.

In stage 1120, responsive to the switching frequency increase of stage1110, the impedance presented to a second of the plurality of secondarywindings of stage 1100 is decreased. Particularly, a secondary sideresonant circuit is coupled in series between the second secondarywinding and a second output. The secondary side resonant circuitcomprises the leakage inductance of the second secondary winding and asecondary side capacitance element. The impedance decrease is responsiveto the leakage inductance and the capacitance of the secondary sidecapacitance of the resonant circuit. Optionally, the resonant frequencyof the secondary side resonant circuit is greater than a maximumswitching frequency of the bridge circuit of stage 1100. Particularly,the switching frequency of the bridge circuit is controlled by aresonant mode controller exhibiting a minimum resonant frequency and amaximum resonant frequency greater than the minimum resonant frequency.The resonant frequency of the secondary side resonant circuit isarranged to be greater than the maximum resonant frequency of theresonant mode controller. In stage 1130, responsive to the switchingfrequency decrease of stage 1110, the impedance of the second output isincreased. Particularly, the impedance increase is responsive to theleakage inductance and the capacitance of the secondary side capacitanceelement of the resonant circuit of stage 1120.

In stage 1140, a first LED luminaire is enabled to provide a firstillumination responsive to a second power signal on the second output ofstage 1120. Particularly, the first LED luminaire is enabled byproviding a current path therethrough. In stage 1150, the provided firstillumination of stage 1140 is regulated. In one embodiment, the providedfirst illumination is regulated by pulse width modulation driving of anelectronically controlled switch, as described below. In anotherembodiment, the provided first illumination of stage 1140 is regulatedby adjusting the resistance of the current path of the first LEDluminaire, such as by increasing the resistance of a transistor coupledin series with the first LED luminaire.

In optional stage 1160, the first LED luminaire of stage 1140 isalternately enabled to provide a first illumination and disabled so asnot provide the first illumination. The regulation of stage 1150comprises the alternate enabling and disabling of the first LEDluminaire. In optional stage 1700, the alternate enabling and disablingof the first LED luminaire of optional stage 1160 is synchronized withthe bridge circuit switching of stage 1100. Optionally, the alternateenabling and disabling of the first LED luminaire is responsive to analternate opening and closing of a first electronically controlledswitch, one of the opening and closing of the first electronicallycontrolled switch being when the voltage across the primary winding ofthe transformer of stage 1100 is substantially zero. In one embodiment,the electronically controlled switch is in series with the first LEDluminaire, the LED luminaire enabled responsive to a closed state of theelectronically controlled switch and disabled responsive to an openstate of the electronically controlled switch. In another embodiment,the electronically controlled switch is in parallel with the first LEDluminaire, the LED luminaire enabled responsive to an open state of theelectronically controlled switch and disabled responsive to a closedstate of the electronically controlled switch.

In optional stage 1180, the second power signal of stage 1140 exhibitsan active portion which provides sufficient voltage to provide the firstillumination and an inactive portion which does not provide sufficientvoltage to provide the first illumination. Optionally, the inactiveportion is a zero voltage portion. The synchronization of optional stage1170 comprises leading edge modulation such that the non-enabled stateof the first illumination of the first LED luminaire is insynchronization with the second output power signal inactive portion. Inthe embodiment where the non-enabled state of the first illumination isresponsive to the first electronically controlled switch of optionalstage 1170, the first electronically controlled switch is switchedduring the second power output power signal inactive portion.Advantageously, as described above, the inactive portion is optionally azero voltage portion and the first electronically controlled switch isswitched when substantially zero voltage is presented thereacrossthereby reducing switching losses.

In optional stage 1190, the synchronization of optional stage 1170comprises falling edge modulation such that the enabling of the firstillumination of the first LED luminaire is in synchronization with thesecond output power signal inactive portion of optional stage 1180.Particularly, the enabling of the first illumination of the first LEDluminaire is during the second output power signal inactive portion andsynchronized with the beginning of the second output power signal activeportion. In the embodiment where the enabling of the first illuminationis responsive to the first electronically controlled switch of optionalstage 1170, the first electronically controlled switch is switchedduring the second power output power signal inactive portion.Advantageously, as described above, the inactive portion is optionally azero voltage portion and the first electronically controlled switch isswitched when substantially zero voltage is presented thereacross.

In optional stage 1200, a second LED luminaire coupled in parallel tothe first LED luminaire of stage 1140 and is alternately enabled toprovide a second illumination and disabled so as not to provide thesecond illumination. The second illumination is enabled responsive tothe second power signal of stage 1120. In optional stage 1210, thesynchronization of optional stage 1170 comprises leading edge modulationsuch that the disabling of the first illumination of the first LEDluminaire is in synchronization with the second output power signalinactive portion of optional stage 1180, as described above in relationto optional stage 1190. Additionally, the alternate enabling anddisabling of the second LED luminaire of optional stage 1200 comprisesfalling edge modulation synchronized with the switching of the bridgecircuit of stage 1100 such that enabling of the second illumination isin synchronization with the second output power signal inactive portion.Particularly, the enabling of the second illumination is during thesecond output power signal inactive portion and synchronized with thebeginning of the second output power signal active portion. Optionally,the enabling of the second LED luminaire is responsive to a secondelectronically controlled switch, the electronically controlled switchbeing switched during the second power signal inactive portion.

In optional stage 1220, one of a plurality of LED luminaires isidentified as the first LED luminaire of optional stage 1160 to becontrolled with leading edge modulation, as described in optional stage1210, and another of the plurality of LED luminaires is identified asthe second LED luminaire of optional stage 1200 to be controlled withfalling edge modulation, as described in optional stage 1210. Theidentification is responsive to an electrical characteristic of each ofthe first and second LED luminaires. Optionally, the electricalcharacteristic is the operating voltage of each of the first and secondLED luminaires.

FIGS. 10A-10B illustrate a high level flow chart of a second LEDluminaire driving method, according to certain embodiments. In stage1300, a primary side electronically controlled switch is switched so asto produce a first output power signal associated with a first of aplurality of secondary windings of a transformer, each of the pluralityof secondary windings of the transformer magnetically coupled to aprimary winding of the transformer. The first power signal is producedat a first output. In stage 1305, the duty cycle of the primary sideelectronically controlled switch is arranged to maintain the firstoutput power signal at a predetermined level. Particularly, the dutycycle of the primary side electronically controlled switch is increasedresponsive to a fall in the first output power signal and the duty cycleis decreased responsive to a rise in the first output power signal.

In stage 1310, a first secondary electronically controlled switch isalternately opened and closed. In stage 1320, responsive to a closedstate of the first secondary electronically controlled switch of stage1310, and further responsive to a second power signal on a second outputassociated with a second of the plurality of secondary windings of stage1300, a first LED luminaire is enabled to provide a first illumination.Optionally, the second output power signal exhibits an active portionwhich provides sufficient voltage to provide the first illumination andan inactive portion which does not provide sufficient voltage to providethe first illumination. Further optionally, the inactive portion is azero voltage portion.

In stage 1330, responsive to an open state of the first secondaryelectronically controlled switch of stage 1310, the first LED luminaireis disabled so as not to provide the first illumination of stage 1320.

In stage 1340, the turns ratio of the first secondary winding of stage1300 and the second secondary winding of stage 1320 is such that poweris delivered to the first output of stage 1300 only when the firstillumination of stage 1320 is not enabled. As described above,optionally a unidirectional electronic valve is arranged between thefirst secondary winding and the first output. As a result, when thefirst illumination is enabled, the voltage at the first secondarywinding is less than the voltage at the first output and theunidirectional electronic valve does not conduct.

In optional stage 1350, the alternate enabling and disabling of thefirst illumination of stages 1320-1330 is synchronized with one offalling edge modulation and leading edge modulation such that theswitching of the first secondary electronically controlled switch to oneof the open and closed states is in synchronization with the optionalsecond output power signal inactive portion of stage 1320, i.e. thefirst secondary electronically controlled switch is switched during thesecond output power signal inactive portion. Advantageously, asdescribed above, the inactive portion is optionally a zero voltageportion and the first secondary electronically controlled switch isswitched when substantially zero voltage is presented thereacross,thereby reducing switching losses.

In optional stage 1360, a second secondary electronically controlledswitch is alternately opened and closed. In optional stage 1370,responsive to a closed state of the second secondary electronicallycontrolled switch of optional stage 1360, and further responsive to thesecond power signal of stage 1320, a second LED luminaire is enabled toprovide a second illumination. The second LED luminaire is coupled inparallel to the first LED luminaire of stage 1320. In optional stage1380, responsive to an open state of the second secondary electronicallycontrolled switch of optional stage 1360, the second LED luminaire isdisabled so as not to provide the second illumination of optional stage1370.

In optional stage 1390, the alternate enabling and disabling of thesecond illumination of optional stages 1370-1380 is synchronized withone of falling edge modulation and leading edge modulation such that theswitching of the second secondary electronically controlled switch toone of the open and closed states is in synchronization with theoptional second output power signal inactive portion of stage 1320, i.e.the second secondary electronically controlled switch is switched duringthe second output power signal inactive portion. Advantageously, asdescribed above the inactive portion is optionally a zero voltageportion and the second secondary electronically controlled switch isswitched when substantially zero voltage is presented thereacross,thereby reducing switching losses.

In optional stage 1400, the turns ratio of the first secondary windingof stage 1300 and the second secondary winding of stage 1320 is suchthat power is delivered to the first output of stage 1300 only whenneither of the first illumination of stage 1320 and the secondillumination of optional stage 1370 are enabled. As described above,optionally a unidirectional electronic valve is arranged between thefirst secondary winding and the first output. As a result, when eitherof the first illumination and the second illumination are enabled, thevoltage at the first secondary winding is less than the voltage thefirst output and the unidirectional electronic valve does not conduct.

It is appreciated that certain features of the invention, which are, forclarity, described in the context of separate embodiments, may also beprovided in combination in a single embodiment. Conversely, variousfeatures of the invention which are, for brevity, described in thecontext of a single embodiment, may also be provided separately or inany suitable sub-combination.

Unless otherwise defined, all technical and scientific terms used hereinhave the same meanings as are commonly understood by one of ordinaryskill in the art to which this invention belongs. Although methodssimilar or equivalent to those described herein can be used in thepractice or testing of the present invention, suitable methods aredescribed herein.

All publications, patent applications, patents, and other referencesmentioned herein are incorporated by reference in their entirety. Incase of conflict, the patent specification, including definitions, willprevail. In addition, the materials, methods, and examples areillustrative only and not intended to be limiting.

It will be appreciated by persons skilled in the art that the presentinvention is not limited to what has been particularly shown anddescribed herein above. Rather the scope of the present invention isdefined by the appended claims and includes both combinations andsub-combinations of the various features described hereinabove as wellas variations and modifications thereof which would occur to personsskilled in the art upon reading the foregoing description and which arenot in the prior art.

1. A circuit for driving at least one light emitting diode (LED)luminaire, said circuit comprising: a resonant mode controller; aconverter comprising a transformer having a primary winding and aplurality of secondary windings each magnetically coupled to saidprimary winding, a bridge circuit arranged to switch responsive to saidresonant mode controller, and a primary side capacitance element inelectrical communication with said primary winding; a first outputassociated with a first of said plurality of secondary windings, saidresonant mode controller arranged to adjust the switching frequency ofsaid bridge circuit so as to maintain said first output at apredetermined level; a second output associated with a second of saidplurality of secondary windings; a secondary side capacitance elementarranged in series between said second of said plurality of secondarywindings and said second output; an LED controller; a first LEDluminaire arranged in cooperation with said first electronicallycontrolled switch to provide a first illumination responsive to a powersignal on said second output; and a first current regulator arranged toregulate current flowing through said first LED luminaire responsive tosaid LED controller.
 2. The circuit according to claim 1, wherein thesecond of said plurality of secondary windings exhibits a leakageinductance, and wherein the combination of the leakage inductance andcapacitance of the secondary side capacitance element forms a resonantcircuit with a resonance greater than a maximum switching frequency ofsaid bridge circuit.
 3. The circuit according to claim 1, wherein saidfirst current regulator comprises a first electronically controlledswitch arranged to be alternately in a closed state and an open stateresponsive to said LED controller, said first LED luminaire arranged toprovide the first illumination when said first electronically controlledswitch is in a first of said closed and open states and not provide thefirst illumination when said first electronically controlled switch isin a second of said closed and open states, and wherein said LEDcontroller is arranged to alternately set said first electronicallycontrolled switch in said first state and said second state insynchronization with said switching of said bridge circuit.
 4. Thecircuit according to claim 3, wherein said second output power signalexhibits an active portion which provides sufficient voltage to providethe first illumination and an inactive portion which does not providesufficient voltage to provide the first illumination, and wherein saidLED controller is arranged to synchronize said alternate opening andclosing of said first electronically controlled switch with leading edgemodulation such that said first electronically controlled switch isswitched to the second of said closed and open states, from the first ofsaid open and closed states, from the first of said closed and openstates, in synchronization with said second output power signal inactiveportion.
 5. The circuit according to claim 3, wherein said second outputpower signal exhibits an active portion which provides sufficientvoltage to provide the first illumination and an inactive portion whichdoes not provide sufficient voltage to provide the first illumination,and wherein said LED controller is arranged to synchronize saidalternate opening and closing of said first electronically controlledswitch with falling edge modulation such that said first electronicallycontrolled switch is switched to the first of said closed and openstates, from the second of said closed and open states, during saidsecond output power signal inactive portion in synchronization with thebeginning of said second output power signal active portion.
 6. Thecircuit according to claim 3, further comprising: a second currentregulator, said second current regulator comprising a secondelectronically controlled switch arranged to be alternately in a closedstate and an open state responsive to said LED controller; and a secondLED luminaire coupled in parallel with said first LED luminaire, saidsecond LED luminaire arranged in cooperation with said secondelectronically controlled switch to provide a second illuminationtherefrom responsive to the power signal from said second output whensaid second electronically controlled switch is in a first of saidclosed and open states and not provide the second illumination when saidsecond electronically controlled switch is in a second of said closedand open states, wherein said second output power signal exhibits anactive portion which provides sufficient voltage to provide the secondillumination and an inactive portion which does not provide sufficientvoltage to provide the second illumination, wherein said LED controlleris arranged to synchronize said alternate closing and opening of saidfirst electronically controlled switch with leading edge modulation suchthat said first electronically controlled switch is switched to thesecond of said closed and open states, from the first of said closed andopen states, in synchronization with said second output power signalinactive portion, and wherein said LED controller is arranged tosynchronize said alternate opening and closing of said secondelectronically controlled switch with falling edge modulation such thatsaid second electronically controlled switch is switched to the first ofsaid closed and open states, from the second of said closed and openstates, during said second output power signal inactive portion insynchronization with the beginning of said second output power signalactive portion.
 7. The circuit of claim 6, wherein said LED controlleris arranged to identify which of a plurality of LED luminairesresponsive thereto is the first LED luminaire, to be controlled withleading edge modulation, and which is the second LED luminaire, to becontrolled with falling edge modulation, responsive to an electricalcharacteristic of each of said first and second LED luminaires.
 8. Amethod of driving at least one light emitting diode (LED) luminaire,said method comprising: switching a bridge circuit so as to produce afirst output power signal, associated with a first of a plurality ofsecondary windings of a transformer, each of the plurality of secondarywindings of the transformer magnetically coupled to a primary winding ofthe transformer, the primary winding of the transformer coupled to aprimary side capacitance element; controlling the frequency of thebridge circuit switching so as to maintain the first output power signalat a predetermined level, by reducing the switching frequency responsiveto a falling first output power signal and increasing the switchingfrequency responsive to a rising first output power signal; responsiveto said increasing of the switching frequency, a leakage inductance of asecond of the plurality of secondary windings, and the capacitance of asecondary side capacitance element arranged in series between a secondoutput and the second of the plurality of secondary windings, decreasingan impedance presented to the second of the plurality of secondarywindings; responsive to said decreasing of the switching frequency, theleakage inductance of the second of the plurality of secondary windings,and the capacitance of the secondary side capacitance element,increasing the impedance presented to the second of the plurality ofsecondary windings; enabling a first LED luminaire to provide a firstillumination responsive to a second power signal on the second output;and regulating said provided first illumination.
 9. The method accordingto claim 8, wherein said frequency controlling is between apredetermined minimum resonant frequency of a resonant mode controllerand a predetermined maximum resonant frequency of the resonant modecontroller, and wherein the secondary side capacitance element and theleakage inductance of the second of the plurality of secondary windingsform a secondary side resonant circuit exhibiting a resonant frequencygreater than the predetermined maximum resonant frequency of theresonant mode controller.
 10. The method according to claim 8, whereinsaid regulating said provided first illumination comprises alternatelyenabling the first LED luminaire to provide the first illumination anddisabling the first LED luminaire so as not to provide the firstillumination, the method further comprising synchronizing said alternateenabling and disabling of the first LED luminaire with said switching ofsaid bridge circuit.
 11. The method according to claim 10, wherein thesecond output power signal exhibits an active portion which providessufficient voltage to provide the first illumination and an inactiveportion which does not provide sufficient voltage to provide the firstillumination, and wherein said synchronizing comprises leading edgemodulation such that said disabling of the first illumination is insynchronization with the second output power signal inactive portion.12. The method according to claim 10, wherein the second output powersignal exhibits an active portion which provides sufficient voltage toprovide the first illumination and an inactive portion which does notprovide sufficient voltage to provide the first illumination, andwherein said synchronizing comprises falling edge modulation such thatsaid enabling of the first illumination is during the second outputpower signal inactive portion in synchronization with the beginning ofthe second output power signal active portion.
 13. The method accordingto claim 10, further comprising alternately enabling a second LEDluminaire, coupled in parallel with the first LED luminaire, to providea second illumination from the second power signal and disabling thesecond LED luminaire so as not to provide the second illumination,wherein the second output power signal exhibits an active portion whichprovides sufficient voltage to provide one of the first and the secondillumination and an inactive portion which does not provide sufficientvoltage to provide any of the first and the second illumination, whereinsaid synchronizing of the first LED luminaire comprises leading edgemodulation such that said disabling of the first illumination is insynchronization with the second output power signal inactive portion,and wherein said alternate enabling and disabling of the second LEDluminaire comprises falling edge modulation synchronized with saidswitching of the bridge circuit such that said enabling of the secondillumination is during the second output power signal inactive portionin synchronization with the beginning of the second output power signalactive portion.
 14. The method of claim 13, further comprisingidentifying which of a plurality of LED luminaires responsive thereto isthe first LED luminaire, to be controlled with leading edge modulation,and which is the second LED luminaire, to be controlled with fallingedge modulation, responsive to an electrical characteristic of each ofsaid first and second LED luminaires.
 15. A circuit for driving at leastone light emitting diode (LED) luminaire, said circuit comprising: aprimary side controller; a flyback converter comprising a transformerhaving a primary winding and a plurality of secondary windings eachmagnetically coupled to said primary winding, and a primaryelectronically controlled switch, said primary electronically controlledswitch arranged to alternately open and close responsive to said primaryside controller, said open and closed state arranged to adjust a currentflowing through said primary winding; a first output associated with afirst of said plurality of secondary windings, said primary sidecontroller arranged to alternately open and close said primaryelectronically controlled switch so as to maintain said first output ata predetermined voltage level; a first unidirectional electronic valvearranged between said first secondary winding and said first output; asecond output associated with a second of said plurality of secondarywindings; an LED controller; a first secondary electronically controlledswitch arranged to be alternately in a open state and a closed stateresponsive to said LED controller; a first LED luminaire arranged incooperation with said first secondary electronically controlled switchto provide a first illumination responsive to a power signal on saidsecond output when said first secondary electronically controlled switchis in said closed state and not provide the first illumination when saidfirst secondary electronically controlled switch is in said open state;and a second unidirectional electronic valve arranged between saidsecond of said plurality of secondary windings and said first LEDluminaire, wherein the turns ratio of said first secondary winding andsaid second secondary winding is such that power is delivered to saidfirst output via said first unidirectional electronic valve only whensaid first secondary electronically controlled switch is switched tosaid open state.
 16. The circuit of claim 15, wherein said second outputpower signal exhibits an active portion which provides sufficientvoltage to provide the first illumination and an inactive portion whichdoes not provide sufficient voltage to provide the first illumination,and wherein said LED controller is arranged to synchronize saidalternate closing and opening of said first electronically controlledswitch with one of falling edge modulation and leading edge modulationsuch that said first secondary electronically controlled switch isswitched to said closed state, from said second state, insynchronization with said second output power signal inactive portion.17. The circuit of claim 16, further comprising: a second secondaryelectronically controlled switch arranged to be alternately in an openstate and a closed state responsive to said LED controller; a second LEDluminaire coupled in parallel with said first LED luminaire, said secondLED luminaire arranged in cooperation with said second secondaryelectronically controlled switch to provide a second illuminationresponsive to the power signal from said second output when said secondsecondary electronically controlled switch is in said closed state andnot provide the second illumination when said second secondaryelectronically controlled switch is in said open state; and a thirdunidirectional electronic value arranged between said second output andsaid second LED luminaire, wherein said LED controller is arranged tosynchronize said alternate opening and closing of said second secondaryelectronically controlled switch with the one of the falling edgemodulation and leading edge modulation such that said second secondaryelectronically controlled switch is switched to one of said closed andopen states in synchronization with said second output power signalinactive portion, and wherein the turns ratio of said first secondarywinding and said second secondary winding are such that power isdelivered to said first output via said first unidirectional electronicvalve only when said first and second secondary electronicallycontrolled switches are both switched to said open states.
 18. An LEDluminaire driving method, the method comprising: switching a primaryside electronically controlled switch so as to produce a first outputpower signal, associated with a first of a plurality of secondarywindings of a transformer, each of the plurality of secondary windingsof the transformer magnetically coupled to a primary winding of thetransformer; adjusting the duty cycle of said switching to maintain thefirst output power signal at a predetermined level; alternately openingand closing a first secondary electronically controlled switch;responsive to said closed state of the first electronically controlledswitch and further responsive to a second power signal on a secondoutput associated with a second of the plurality of secondary windings,enabling a first LED luminaire to provide a first illumination; andresponsive to said open state of the first secondary electronicallycontrolled switch, disabling the first LED luminaire so as not toprovide the first illumination, wherein the turns ratio of the firstsecondary winding and the second secondary winding is such that power isdelivered to the first output from the transformer only when said firstillumination is not enabled.
 19. The method according to claim 18,wherein the second output power signal exhibits an active portion whichprovides sufficient voltage to provide the first illumination and aninactive portion which does not provide sufficient voltage to providethe first illumination, the method further comprising synchronizing saidenabling and disabling of the first LED luminaire with one of fallingedge modulation and leading edge modulation such that said switching ofthe first secondary electronically controlled switch to one of saidclosed and open states is in synchronization with the second outputpower signal inactive portion.
 20. The method of claim 19, furthercomprising: alternately opening and closing a second secondaryelectronically controlled switch; responsive to said closed state of thesecond secondary electronically controlled switch and further responsiveto the second power signal, enabling a second LED luminaire, coupled inparallel to the first LED luminaire, to provide a second illumination;responsive to said open state of the second secondary electronicallycontrolled switch, disabling the second LED luminaire so as not toprovide the second illumination; and synchronizing said enabling anddisabling of the second LED luminaire with said inactive portion of saidsecond output power signal, said synchronizing comprising one of fallingedge modulation and leading edge modulation such that said switching ofsaid second secondary electronically controlled switch to one of saidclosed and open states is in synchronization with said second outputpower signal inactive portion, wherein the turns ratio of the firstsecondary winding and the second secondary winding is such that power isdelivered to the first output from the transformer only when neither ofsaid first illumination and said second illumination are enabled.